The present invention relates to a method for controlling fuel injection in an internal-combustion engine.
In the engine sector, there is felt the need to make injections of fuel in which the instantaneous flow rate of injected fuel as a function of time comprises at least two stretches with levels that are substantially constant and different from one another, i.e., it can be represented schematically by a curve of the “stepwise” type. In particular, there is felt the need to inject an instantaneous flow of fuel having a plot in time T similar to the one represented by the curve of FIG. 1, in which there is present a first level L1 and a subsequent second level L2 higher than the first.
In an endeavour to obtain said flow-rate curve, it is known to provide injectors of a dedicated type, in which opening of the injection nozzle is caused by the lifting of two movable open/close pins co-operating with respective springs, or else by the lifting of a single movable open/close pin co-operating with two coaxial springs. In particular, the two springs are differently preloaded with respect to one another, and/or present characteristics of force/displacement that are different from one another, for opening the nozzle with lifts such as to approximate the required flow-rate curve.
The known solutions just described are far from altogether satisfactory in so far as it is somewhat complex to calibrate the springs in an optimal way to obtain a first level or step of flow rate smaller than the maximum flow rate from the nozzle and, hence, to approximate a flow-rate curve like the one of FIG. 1.
Furthermore, given the same pressure of supply of the fuel, once the law of lifting of the pins and, hence, the law of opening of the nozzle, has been established, the profile of flow rate of injected fuel is not modifiable as the operating conditions of the engine vary between the various injections performed by the injector.
In addition, it is somewhat difficult to obtain injectors with a profile of flow rate of injected fuel constant for the entire production.
The purpose of the present invention is to provide a method for controlling fuel injection in an internal-combustion engine which will enable the drawbacks set forth above to be overcome in a simple and economically advantageous way.
According to the present invention, a method is provided for controlling fuel injection in an internal-combustion engine provided with an electroinjector comprising:                an electroactuator; and        an atomizer, comprising an injection nozzle and a pin, which is movable along an opening stroke and a closing stroke for opening/closing said nozzle under the control of said electroactuator; the electroinjector performing dosage of the fuel by modulating in time opening of the pin of the atomizer according to the pressure of supply of the electroinjector itself;the method being characterized by supplying to said electroactuator a first electrical command and at least a second electrical command that are sufficiently close to one another as to displace said pin with a profile of motion without any discontinuity in time, and such as to cause said pin to perform a first opening displacement and a second opening displacement, respectively.        